push outward, when it expands, what happens to the temperature in the middle of that? drop. and that drops. so the reason for it expanding is because it was going from a region of higher pressure to lower pressure? excellent, excellent, excellent. the reason it expands is because the air goes from a region of high pressure, down here, deep, deep down in the bottom of this ocean of air. and when it rises, what's it gonna do? like the balloon, like the fish, like the scuba diver we've all talked about-- these ideas are all connected, gang, huh? and as it goes up, up, up, it's gonna expand. and we learned a new thing today. as it expands, son of a gun, it cools. why does it cool? because the molecules in the middle are making impact with things on the average that are going away. and so they rebound with less, less, less speeds. and the effect is big. i mean, it's quite noticeable. there's a third form of heat transfer, gang. and the third form-- not conduction, not convection but what? radiation.